The overall power loss of power IGBTs that occurs during operation can be reduced by providing an n-doped field stop zone which is doped more highly than the n-type base and precedes the p-type emitter or collector. Such field stop zones preceding the p-type emitter and of the same conduction type as the n-type base, which are also referred to as buffer zones, are employed particularly in so-called PT-IGBTs (PT=punch through) and serve for limiting the electric field in order to prevent the electric field from punching through to the p-type emitter.
Nakagawa, A. et al: “MOSFET-mode Ultra-Thin Wafer PTIGBT for Soft Switching Application—Theory and Experiments”, Proceedings of ISPSD 2004 (Kitakyushu, Japan), pages 437-440, describes a so-called SPT-IGBT (SPT =soft punch through) with an n-type buffer zone preceding the p-type emitter.
DE 100 53 445 C2 describes a power IGBT whose p-type emitter is preceded by an n-doped field stop zone which is doped more highly than the n-type base and which has a more highly doped section adjoining the p-type emitter and a more weakly doped section adjoining the more highly doped section.
For the production of power semiconductor components in thin wafer technology, it is known firstly to provide a semiconductor wafer—from which the individual chips are later sawn out—the thickness of which is greater than the desired thickness of the later components, and to reduce the thickness of, i.e. to thin, the wafer in the course of the production method. In this case, it is desirable to carry out as many process steps as possible—for example including the process steps for producing such a field stop zone—prior to the thinning in order that the wafer, which is less stable mechanically after the thinning, is thermally or mechanically loaded as little as possible.
A semiconductor body can be thinned in a known manner by grinding thin the semiconductor body, by grinding thin and subsequently etching the semiconductor body, or just by etching the semiconductor body.
One possibility for realizing such an n-doped semiconductor zone is customarily the indiffusion of phosphorus into the semiconductor body. However, this method has the disadvantage that, on account of the low diffusion constant of phosphorus, diffusion processes with extremely long diffusion durations at very high temperatures have to be carried out in order to achieve high penetration depths such as are required for the production of a field stop zone prior to thinning the wafer. The diffusion duration for the production of an n-doped zone with a penetration depth of approximately 200 μm is several weeks at diffusion temperatures far in excess of 1200° C.
The long diffusion duration and the high diffusion temperature result in severe loading on the semiconductor body to the effect that a high oxygen concentration arises in the semiconductor body, which may be disadvantageous both with regard to an undesirable formation of so-called thermal donors and with regard to the generation of disturbing recombination and generation centers. Moreover, the gradient of the doping profile of the n-doped semiconductor zone formed by the diffusion process cannot be reduced arbitrarily since the diffusion durations that are long anyway would rise even further as a result of this.
DE 198 29 614 A1 describes a method for producing a field stop layer of an IGBT, which provides for producing the stop layer by means of a diffusion method firstly with a thickness that is greater than is electrically necessary, and for subsequently thinning the component in order to obtain the desired thickness of the stop layer.
A method for producing a buried field stop zone by means of ion implantation is described for example in 102 43 758 A1.